“His potential is greater and higher than Everton as a final destination,” Koeman told Belgian newspaper HLN.

“If Romelu was to play at Everton until the end of his career I know he has left something behind,” added the Dutchman, 53.

“I gave him confidence and he has himself recognised that it was good for his development to play another year at Everton. What after this season comes, no-one knows.”

Everton have indicated they are willing to offer Lukaku a long-term contract that would make him their highest-paid player.

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Ronald Koeman has compared Lukaku with former Barcelona and Netherlands striker Patrick Kluivert

Lukaku, who is under contract until 2019, first joined Everton on loan from Chelsea and has 68 goals for the Merseyside club in 137 appearances.

His 50 goals puts him third on Everton’s list of top scorers in the Premier League era, behind Tim Cahill on 56 and Duncan Ferguson on 60.

Lukaku has scored 17 goals at international level and Koeman has drawn comparisons with former Netherlands striker Patrick Kluivert, who he worked with during spells coaching with the national side, at Barcelona and later as manager at PSV.

Kluivert scored 40 goals in 79 games for the Netherlands and is the director of football at Paris St-Germain.

Koeman added: “Kluivert was also a striker who was quite young when he was in the picture and had a fantastic career. Eventually Kluivert played for Barcelona, which could happen with Lukaku.

“I think Lukaku is quite complete. He can hold a ball and be a target man and, because he is tall and physically strong, you can play directly with the long ball.”